Modern computed tomography (CT) scanners have the goal of covering a large volume of the patient in a single rotation at very fast rotation speeds. This objective is driven by demands of cardiac CT to cover the entire organ in less than a heartbeat. Impressive results have been achieved with the current generation of CT scanners. However, the downside of this development is the increased dose to the patient, the increase in scatter, and the degradation of image quality in the outer slices due to cone beam artifacts. In particular, the increased dose in medical imaging has come under scrutiny, with several published studies documenting the elevated risk of cancer resulting from the radiation involved in medical imaging.
The manufacturers of CT scanners are attempting to address dosage concerns with new developments. One common avenue being pursued is the use of photon counting detectors. Photon counting detectors have intrinsically higher detective quantum efficiency (DQE) than integrating detectors and have a bias towards lower photon energies. These qualities lead to increased image contrast, resulting in lower dose while maintaining image quality. Even more contrast enhancement and dose reduction can be achieved with the use of energy-resolving detectors. However, photon counting and energy resolving detectors are significantly more expensive than integrating detectors. This increased cost is particularly challenging for conventional CT scanners that rely on detectors with very large areas.
CT manufacturers are exploring a variety of other methods to reduce this dose while maintaining image quality. However, these improvements are expected to be minor compared to that which may be gained by an alternative CT system concept, inverse-geometry CT (IGCT). Conventional CT utilizes a single focal spot X-ray source and a large-area detector, whereas IGCT utilizes a large-area, multi-focal spot X-ray source and a small-area detector. IGCT offers higher dose efficiency and faster acquisition times than state-of-the-art conventional CT systems. Thus, IGCT has the potential to overcome disadvantages with conventional CT and significantly out-perform conventional CT scanners.
In conventional CT scanners, each projection is of the entire field of view and is obtained with a single focal-spot X-ray source and a large detector. By contrast, inverse geometry systems utilize a large-area scanned X-ray source and a field-of-view projection is composed of many narrower projections each acquired with a different detector location. The detector in an IGCT system is quite small compared to that in a conventional CT system. Thus, it is economically feasible to implement advanced yet more expensive detector technologies in IGCT. However, IGCT faces difficulties in implementation due to a large source array to be rotated at high speeds and significant challenges from high power and cooling requirements of the source.
What is needed is a CT imaging system capable of producing rapid high quality images. Furthermore, the CT imaging system should reduce the effects of cone beam artifacts.